Solar heat responsive exterior surface covering

ABSTRACT

An exterior surface covering has a colored outer layer that transmits infrared radiation and an inner layer with a thermochromic pigment that absorbs heat at low temperature and reflects at high temperatures. The outer layer conceals the color change of the thermochromic pigment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of pending U.S. patent applicationSer. No. 12/782,329, filed on May 18, 2010; which is a continuation ofU.S. patent application Ser. No. 11/456,112 filed on Jul. 7, 2006, nowU.S. Pat. No. 7,749,593.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to surface coverings such as coatings forexterior building materials such as exterior cladding including sidingmaterial, roofing shingles, roofing membranes, and the like.

2. Brief Description of the Prior Art

It is well known that surfaces with dark colors will absorb significantamounts of solar heat from solar radiation, while light or white colorswill reflect more solar radiation and hence produce lower surfacetemperatures under the sun. This is particularly true for a buildingenvelope or building claddings, such as roofing and siding materials. Inthis case darker colors can absorb significant amount of solar heat andthus increase the energy required for cooling the interior during hotseasons.

Reduced energy consumption is an important national goal. For example,the State of California has a code requirement that all commercialroofing materials in low-slope applications need to exceed a minimum of70% solar reflectance in order to meet California's energy budget code.Also, in order to qualify as Energy Star® roofing material, a roofingmembrane needs to exceed 65% solar reflectance.

To reduce the solar heat build-up at exposed building surfaces orroofing assemblies, one may consider using light colors, or theso-called “cool coloring technology” with reflective properties in thenear infrared of solar radiation to reduce solar heat absorption.However, such solutions will result in energy penalty during coldseasons, where heating energy demand can be increased due to loss ofsolar heat absorption. While in some climates, such as southernCalifornia, solar heat resistance is the prime if not exclusiveconsideration, in most of the United States there is a significantenergy demand for heating during much of the year.

Thus, it is advantageous to have a colored surface that can not onlyprovide aesthetic values to a structure, but also optimize the solarenergy absorption/reflection in order to maximize whole building energyefficiency by adjusting its solar reflectance in response to the changeof surrounding temperatures.

This problem has been addressed by using thermochromatic orthermochromic colorants that can change from dark to light colors assurface temperature changes.

For example, U.S. Pat. No. 5,571,596 discloses a roofing shingle whichpreferably includes a topcoat of a thermo-chromatic pigmented paintwhich changes color with temperature, lightening in strong sunlight toreflect heat and darkening during cool shady days to absorb heat. U.S.Pat. No. 6,500,555 discloses thermochromic laminates for use in roofingand siding to control the temperature of an underlying structure. U.S.Patent Application Publication No. 2005/0064175 disclosesmicroencapsulated thermomorphic materials that can be applied to roofsin situ or to the exterior surfaces of shingles, as well aselectorphoretic panels that can be applied over existing roofs toachieve a controllable color change. However, thermochromatic colorantscan result in color change of the surfaces. Such color changes may notbe desirable for exposed building surfaces where aesthetic appearance isimportant. U.S. Pat. No. 6,647,688 discloses providing a luminescentmaterial in vinyl siding or trim so that the siding or trim may absorblight during the daytime and glow at night.

Depending on local temperature fluctuations, a surface covered with asubstance containing a thermochromic pigment may experience colorvariation that the consumer may find very objectionable. Also, it isknown that thermochromatic colorants are generally not sufficientlylightfast for use in applications subject to outdoor weatheringexposure.

Other approaches to building temperature control include systems withretractable film or textiles mounted to the rooftop or claddings tomanage the solar heat absorption in order to maximize building energyconsumption during hot/cold seasons.

In other systems, water circulation or water evaporation have been usedto control the surface temperature of exterior structures.

U.S. Pat. No. 6,446,402 discloses thermochromic window materials thatsubstantially block solar radiation when the ambient temperature is highand allow sunlight to enter when the ambient temperature is low.

There is a continuing need for exterior surfacing material such asroofing materials that have improved solar reflectance while providingand maintaining an attractive appearance. Further, there is a continuingneed for surfacing materials that contribute to energy saving in boththe cooling season and the heating season.

SUMMARY OF THE INVENTION

The present invention provides a surface covering having controllablesolar heat absorption and reflection properties.

The surface covering is useful as a part of roofing or building claddingcomponents, siding or other covering, and in fencing, decking andrailing applications, as well. It can also be employed as a surfacecovering for roofing granules included in roofing shingles. Further, thesurface covering of the present invention can be employed in otherapplications where control of heat buildup due to absorption orreflection of solar radiation is desired, such as, for example,automotive or aerospace coatings.

The present invention also provides a method of making a surfacecovering having controllable solar heat absorption and reflectionproperties.

Further, the present invention also provides methods and systems forcontrolling solar heat absorption and reflection properties of asubstrate subject to incident solar radiation.

The present invention provides an exterior surface covering such as acoating comprising an outer layer having a transmission coefficient ofat least 50 percent for electromagnetic radiation in the wavelength ragefrom 700 nanometers to 2500 nanometers, and an inner layer having areflectance for electromagnetic radiation in the wavelength range from700 nanometers to 2500 nanometers. The outer layer of the exteriorsurface covering is preferably colored, for example, to achieve adesired aesthetic effect. The reflectance of the inner layer isdependent on a variable parameter, and varying by a factor of at least0.5 as the parameter is varied over a predetermined range. In one aspectof the present invention, the reflectance increases with an increase inthe parameter over the predetermined range of the parameter. In anotheraspect of the present invention, the reflectance increases with adecrease in the parameter over the predetermined range of the parameter.

In one presently preferred embodiment of the present invention, thevariable parameter is temperature. In this case, it is preferred thatthe reflectance increase as the temperature increases. Preferably, thereflectance varies from less than 0.2 to greater than 0.25 when thetemperature varies from less than 20 degrees C. to greater than 30degrees C.

Preferably, the inner layer comprises at least one thermochromicsubstance.

In the various embodiments of the present invention, when an at leastone thermochromic substance is included in a specific layer, it ispreferred that the at least one thermochromic substance be selected fromthe group consisting of thermochromatic colorants, thermochromaticpolymers, composite thermochromatic pigments, chromogenic thermotropicgels, vanadium oxides, polythiophene polymers, liquid crystals,spirobenzopyrans, spironaphthoxazines, chromenes, fulgides, anddiarylethenes.

In another aspect of the present invention, the variable parameter isthe strength of an applied electric field and the inner layer comprisesan electrochromic substance. In this case, it is preferred that thereflectance vary from less than 0.2 to greater than 0.25 when thestrength of the applied electric field exceeds a predetermined fieldstrength.

In a second embodiment, the present invention provides an exteriorsurface covering comprising three layers. In this embodiment, theexterior surface covering includes an outer colored layer having atransmission coefficient of at least 50 percent for electromagneticradiation in the wavelength rage from 700 nanometers to 2500 nanometers.In addition, the exterior surface covering comprises a middle layerhaving a transmission coefficient for electromagnetic radiation in thewavelength range from 700 nanometers to 2500 nanometers, with thetransmission coefficient being dependent on a variable parameter, andthe transmission coefficient varying by a factor of at least 0.5 as theparameter is varied over a predetermined range. The exterior surfacecovering also includes an inner layer having a reflectance of at least40 percent for electromagnetic radiation in the wavelength range from700 nanometers to 2500 nanometers. In one aspect of this embodiment, itis preferred that the transmission coefficient of the middle layerincreases with an increase in the parameter over the predetermined rangeof the parameter. In another aspect of this embodiment of the presentinvention, it is preferred that the transmission coefficient of themiddle layer increases with a decrease in the parameter over thepredetermined range of the parameter.

In a presently preferred embodiment, the variable parameter istemperature. Preferably, the transmission coefficient of the middlelayer varies from less than 0.4 to greater than 0.5 when the temperaturevaries from less than 20 degrees C. to greater than 30 degrees C.

In this embodiment of the present invention, it is preferred that themiddle layer comprises at least one thermochromic substance.

In another aspect of this embodiment of the present invention, it ispreferred that the variable parameter is the strength of an appliedelectric field and the middle layer comprises an electrochromicsubstance. In this embodiment, it is preferred that the transmissioncoefficient of the middle layer vary from less than 0.4 to greater than0.5 when the strength of the applied electric field exceeds apredetermined electric field strength.

In a third embodiment, the present invention provides an exteriorsurface covering including three layers, which include an outer coloredlayer having a transmission coefficient of at least 50 percent forelectromagnetic radiation in the wavelength rage from 700 nanometers to2500 nanometers, as well as a middle layer having a transmissioncoefficient for electromagnetic radiation in the wavelength range from700 nanometers to 2500 nanometers, the transmission coefficient beingdependent on a variable parameter, and the transmission coefficientvarying by a factor of at least 0.5 as the parameter is varied over apredetermined range. In addition, this embodiment of the presentinvention includes an inner layer having an absorption coefficient atleast 60 percent for electromagnetic radiation in the wavelength rangefrom 700 nanometers to 2500 nanometers. In one aspect of thisembodiment, it is preferred that the transmission coefficient of themiddle layer increases with an increase in the parameter over thepredetermined range of the parameter. In another aspect of thisembodiment of the present invention, it is preferred that thetransmission coefficient of the middle layer increases with a decreasein the parameter over the predetermined range of the parameter.

In a presently preferred embodiment, the variable parameter istemperature. Preferably, the transmission coefficient of the middlelayer varies from less than 0.4 to greater than 0.5 when the temperaturevaries from less than 20 degrees C. to greater than 30 degrees C.

In this embodiment of the present invention, it is preferred that themiddle layer comprises at least one thermochromic substance.

In another aspect of this third embodiment of the present invention, itis preferred that the variable parameter is the strength of an appliedelectric field and the middle layer comprises an electrochromicsubstance. In this embodiment, it is preferred that the transmissioncoefficient of the middle layer vary from less than 0.4 to greater than0.5 when the strength of the applied electric field exceeds apredetermined electric field strength.

In a fourth embodiment, the present invention provides an exteriorsurface coating including an outer layer having a transmissioncoefficient of at least 50 percent for electromagnetic radiation in thewavelength rage from 700 nanometers to 2500 nanometers, as well as amiddle layer having a transmission coefficient for electromagneticradiation in the wavelength range from 700 nanometers to 2500nanometers, the transmission coefficient being dependent on a firstvariable parameter, the transmission coefficient varying by a factor ofat least 0.5 as the first variable parameter is varied over apredetermined range. The present embodiment also includes an inner layerhaving an absorption coefficient for electromagnetic radiation in thewavelength range from 700 nanometers to 2500 nanometers, the absorptioncoefficient being dependent on a second variable parameter, and theabsorption coefficient varying by a factor of at least 0.5 as the secondvariable parameter is varied over a predetermined range.

In one presently preferred embodiment, the surface covering of thepresent invention comprises at least two coating layers, applied to asubstrate as fluid coating compositions, to provide an exterior surfacecoating to the substrate. In another presently preferred embodiment, thesurface covering of the present invention comprises a covering materialcomprising a first film layer, and at least one additional layer formedfrom a second film layer laminated to the first film layer, or at leastone additional layer formed from a coating composition.

In another aspect, the present invention provides roofing granulescoated with an exterior surface coating according to the presentinvention. In another aspect, the present invention provides asphaltshingles with an exterior surface coated with an exterior surfacecoating according to the present invention. In yet another aspect, thepresent invention provides a bituminous sheet-roofing product with anexterior surface covering according to the present invention. In afurther aspect, the present invention provides wall cladding such aspolymeric siding material, for example, polyvinyl chloride,polypropylene, or the like, or fiber cement siding with an exteriorsurface covering according to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional elevational view of a first embodimentof an exterior surface covering according to the present invention.

FIG. 2 is a schematic sectional elevational view of a second embodimentof an exterior surface covering according to the present invention.

FIG. 3 is a schematic sectional elevational view of a third embodimentof an exterior surface covering according to the present invention.

FIG. 4 is a schematic sectional elevational view of a fourth embodimentof an exterior surface covering according to the present invention.

DETAILED DESCRIPTION

By employing the surface covering of the present invention, the solarheat absorption of a surface, such as, for example, a building envelope,can be optimized for better energy efficiency during heating/coolingseasons by changing its solar reflectance in the NIR radiation range inresponse to surrounding temperature or weather changes without affectingits surface color.

This objective can be achieved, for example, by the combination of acolor topcoat that allows the majority of solar radiation in the nearinfrared range to pass through, and a second layer that changes itssolar reflectance in response to surrounding temperatures or otherweather-related stimuli.

Referring now to the figures in which like reference numerals representlike elements in each of the several views, there is shown in FIG. 1 aschematic sectional elevational view of a first embodiment of anexterior surface covering 10 according to the present invention. Theexterior surface covering 10 is applied over a substrate 28 andcomprises an outer layer 20 of a protective topcoat and an innerthermochromatic or thermochromic layer 22 between the outer layer 20 andthe substrate 28.

The topcoat or outer layer 20 is transmissive to near infrared radiationand has a desirable apparent color due to absorption and reflection inthe visible spectrum. The inner layer 22 changes color with temperature.At lower temperatures, below a first temperature T₁, the inner layer 22may absorb at least a portion of the incident infrared radiation asheat, and may transmit at least a portion of the incident infraredradiation to the substrate 28 to be absorbed by the substrate 28.However, at such lower temperatures, the inner layer 22 has a lowreflectance for near infrared radiation.

At higher temperatures, above a second temperature T₂, the inner layer22 changes color so that its reflectance increases in the near infraredregion, and the inner layer 22 acts to reflect heat transmitted throughthe topcoat or outer layer 20 back through the topcoat 20 and away fromthe underlying substrate 28.

When the inner layer 22 changes its color or reflectance properties, theoutwardly visible topcoat 20 maintains the appearance of the coatedsubject such that the change is not objectionably visibly discernible.

A schematic sectional elevational view of a second embodiment of anexterior surface covering 30 according to the present invention isprovided in FIG. 2. The exterior surface covering 30 of this embodimentalso includes an outer or top layer 40, and an inner layer 42. In thisembodiment, the inner layer 42 exhibits a change in color ortransmissivity. However, in this exterior surface coating 30 the innerlayer 42 is an electrochromic layer rather than a thermochromic layer asin the case of the exterior surface covering 10 of the first embodiment.

In this second embodiment, a pair of thin films 46 of an electrochromicpolymer bracket the inner layer 42. These films 46 serve as electrodesfor applying an electric field to the inner layer 42. Suitable means forgenerating, applying and controlling an electrical potential areprovided (not shown) and connected to the thin films 46. One film 46 isinterposed between the upper layer or topcoat 40 and the inner layer 42,while a second film 46 is interposed between the inner layer 42 and thesubstrate 48. The inner layer 42 has either absorptive or reflectiveproperties, depending whether an electric filed of a predeterminedstrength is being applied. In one embodiment, when an electrical fieldof a predetermined field strength is applied, the inner layer 42 istransparent to infrared radiation, thus allowing heat to reach thesubstrate 48 to be absorbed or reflected, depending on the nature of thesubstrate 48. When the electric field is removed, the inner layer 42changes to an opaque layer 42 that can absorb or reflect the heatdepending on its composition.

A third embodiment of an exterior surface covering 50 according to thepresent invention is shown in the schematic sectional elevational viewof FIG. 3. In this third embodiment the exterior surface covering 50includes three layers 60, 62, 64. In this embodiment, an outer or firstlayer 60 serves as a protective topcoat and includes colorants havinglow or non-absorbing properties in the near infrared region. Theexterior surface covering 50 also includes a middle or second layer 62that has reflectance properties that change with changing temperature.Finally, the exterior surface covering 50 also includes an inner orthird layer 64 that is highly reflective. In this case, thethermochromic effect color or reflectivity change of the second layer 62is such that at high temperatures the second layer becomes transparent.This transparency then allows light from the near infrared spectrumpassing through the first or outer layer 60 to pass also through thesecond layer 62 to be reflected away from the substrate 68 by the highlyreflective third layer 64. In this way, at higher temperatures, theexterior surface structure 50 is more highly reflective of excess heatfrom the near infrared region of solar radiation.

A fourth embodiment of an exterior surface covering 70 according to thepresent invention is shown in the schematic sectional elevational viewof FIG. 4. In this fourth embodiment the exterior surface covering 70includes three layers 80, 82, 84 covering a substrate 88, as in the caseof the third embodiment. In this fourth embodiment, an outer or firstlayer 70 is provided as a protective topcoat and also includes colorantshaving low or non-absorbing properties in the near infrared region.However, in this fourth embodiment of the exterior surface covering 70,the innermost or third layer 84 is highly absorptive. In this case, thethermochromic effect color or reflectivity change of the middle orsecond layer 82 is such that at low temperatures the second layer 82becomes transparent. This transparency then allows light from the nearinfrared spectrum passing through the first or outer layer 80 to alsopass through the second layer to be absorbed by the highly absorptivethird layer 84. In this way, at lower temperatures, the exterior surfacecovering 70 is more highly absorptive of heat from the near infraredregion of solar radiation and the exterior surface covering 70 cancapture thermal energy. At higher temperatures, the exterior surfacecovering 70 is less absorptive. In some cases, it is advantageous toprovide a second layer 82 that becomes reflective to infrared radiationat elevated temperatures.

The exterior surface covering of the present invention can be preparedby formulating coating compositions for use in forming layers with thedesired optical characteristics. For example, in the case of the firstembodiment of the present invention, a first coating composition can beformulated to include at least one suitable thermochromic pigmentdispersed in a suitable first polymeric binder, and a second coatingcomposition including a suitable colorant dispersed in a suitable secondpolymeric binder.

The polymeric binder employed for the first coating composition can bethe same as or differ from the polymeric binder employed for the secondcoating composition. Preferably, the polymeric binder is selected toinclude a polymeric material having good exterior durability, such as apoly(meth)acrylate. In addition, it is preferred that the polymericbinder employed for the second coating composition have goodtransparency in the near infrared.

The polymeric binders employed can be solvent-based materials. However,water-based polymeric binders such as acrylic latex binders arepreferred in the interest of reducing solvent emissions. When awater-based polymeric binder is employed, conventional coatingsadditives for water-based coatings compositions can be included, such aswater, cosolvents, thickeners, rheology modifiers, agents for promotingfilm formation and coalescence, biocides, fungicides, fire retardantmaterials, and the like.

The exterior surface coating is formed by initially applying the firstcoating composition to the surface of the substrate by a suitableapplication means. The application means can employ conventionalcoatings application equipment, such as spray, roller, dip, curtain, orbrush coating devices. Next, the first coating composition is cured toform an inner covering layer. The specific requirements of the curingprocess depend upon the components of the first coating composition. Forexample, when a water-based polymeric binder such as a water-basedacrylic polymeric latex material is employed for preparing the firstcoating composition, the first coating composition can be sprayed on thesurface of the substrate to a predetermined thickness. Cure isaccomplished by simply permitting the first coating composition toprogress through water loss, film formation, coalescence of the latexparticles, etc.

Next, the second coating composition is applied over the surface of theinner covering layer by suitable application means. The second coatingcomposition includes a polymeric binder having good transparency to nearinfrared radiation, such as poly(meth)acrylate materials. Preferably,the second coating composition also includes at least one ultravioletabsorbent material. The second coating composition preferably alsoincludes at least one colorant for achieving a desired aesthetic effect.When a water-based acrylic polymeric latex material is employed toformulate the second coating composition, the second coating compositioncan be sprayed on the surface of the cured inner covering layer at apredetermined thickness, and permitted to cure by loss of water and filmformation.

In the case of those embodiments of the present invention requiringthree layers, each such layer can be formed from a corresponding coatingcomposition. Each such corresponding coating composition can in turn beapplied to the suitable surface by conventional coating techniques, andpermitted to cure to form a corresponding exterior surface coveringlayer.

While the exterior surface covering of the present invention can beprepared by the successive application of suitable coating compositionsto the substrate surface, other methods of forming the exterior surfacecovering can also be employed. For example, in the case of the firstembodiment of the exterior surface coating of the present invention, theinner layer can be formed from a suitable first film material in which athermochromic pigment is dispersed. Examples of film materials that canbe used include acrylics, polyurethanes, vinyls, olefin polymers andcopolymers, and fluorinated polymers. The outer layer can be formed froma suitable second film material in which a colorant has been dispersed,and the exterior surface covering can be formed by laminating the firstfilm material to the second film material using a suitable laminationprocess which may include the use of a lamination adhesive. The exteriorsurface covering can be subsequently applied to the substrate surface byapplication of an adhesive coating to the substrate surface, followed byapplication of the exterior surface covering. In another aspect, anadhesive material can be applied to the interior surface of the exteriorsurface covering, and the interior surface then covered with a suitablerelease liner. When installing the exterior surface covering, theexterior surface covering is trimmed to match the substrate surfacebeing covered, the release liner is removed from the back of theexterior surface covering, and the exterior surface covering is thenapplied in registration to the substrate surface. In the alternative,the exterior surface covering can be secured to the substrate surfacemechanically, such as by fasteners.

In a further variation, the exterior surface covering is formed byapplying a coating composition to a film forming at least one layer ofthe exterior surface covering. The coating composition is then cured toprovide a second layer.

In another example, at least one layer of the exterior surface coveringand the substrate are formed from a polymeric material and are formedsimultaneously by a polymer forming process such as coextrusion. Forexample, when the exterior surface covering is being applied to buildingcladding such as polyvinyl chloride siding material, the PVC sidingsubstrate and the inner layer of the exterior surface covering can becoextruded using conventional plastics extrusion equipment. The outerlayer of the exterior surface covering can then be formed on the surfaceof the inner layer by applying a coating composition including thedesired colorant material.

The colored topcoat can not only provide aesthetically desirable colors,but also provide weatherability and UV protection for the underlyinglayer(s). Since the topcoat has high transparency in the near infraredrange of solar radiation, the solar heat absorption of the exteriorsurface covering can be controlled by the underlying portion of thecovering. Hence, the color of the exterior surface covering can remainwithin a desired predetermined range or band, or even the same, even ifthe inner layer changes its color in order to optimize solar absorption.

Suitable topcoats can be prepared by using the colorants that have hightransparency to near infrared radiation. Examples of such colorantsinclude, but are not limited to, pearlescent pigments, lamellar effectpigments, metal/metal oxide coated mica or glass particles, organicpigments, perylene pigments, ultramarine blue pigments, ornano-pigments.

The inner layer preferably has solar reflectance that varies in responseto changes in surrounding temperatures or other environmental stimuliduring heating/cooling seasons.

Material properties that can provide such reversible changes in solarreflectance may include, but are not limited to, thermochromism,photochromism, electrochromism, solvatochromism, ionochromism,halochromism, crystalline polymorphism or changes in refractive indices.

Examples of such systems comprise thermochromatic colorants,thermochromatic polymers, composite thermochromatic pigments,chromogenic thermotropic gels, vanadium oxides, polythiophene polymers,liquid crystals, spirobenyopyrans, spironaphthoxazines, chromenes,fulgides, diarylethenes, or electrochromic chemicals. Depending on theirchemical reactivity, thermochromic materials can either be addeddirectly to a coating composition, or first microencapsulated beforeaddition in order to chemically isolate the thermochromic material fromother components of the coating composition. Techniques formicroencapsulating target materials are well known in the art. U.S.Patent Application Publication No. 2005/0064175 discloses intrinsicallythermochromic materials including spirooxazines, stereoisomorphiccompounds such as biathrylidenes including bianthrones,bithioanthylidenes, and dixanthylidenes, polythiophenes, polysilanes,and poly diacetylenes, photochromic materials which require auxiliarymaterials such as temperature-sensitive UV blocking agents to achievethermochromism, including spironaphthoxazines, benzopyrans,naphthopyrans, fulgides, diarylethenes, dihydroindolizines,dithiophenylperfluorocyclopentenes, and spirobenzopyrans; ioniochromicmaterials such as phthalides such as phthaleins includingphenylphthalein, crystal violet lactone, and pyridyl blue,leucotriarylmethanes, azo dyes, styryl dyes, chelates includingdimethylgyloxime, 1,2-dihydrobenzenes, 1-hydroxyanthraquinones, crownethers, mono- and di-vinylphthalides including monovinylphthalides,diarylphthalides, fluorenes, fluorans, lactams, and sulfones.

In some embodiments of the present invention, the inner portion of thecovering can include a bottom layer of reflective material, such aswhite coating or metal/metallized layer, and an upper layer that changesfrom opaque to transparent by the stimuli of outdoor environments suchas temperature.

The exterior surface coverings of the present invention for optimizingsurface solar reflectance and energy efficiency of a building assemblycan be directly applied to the existing exterior envelope throughtypical coating application methods, or they can be part of thecladdings that are applied to the exterior envelope separately.

Depending on the coverage of the top or outermost layer, there could besome lightening, or darkening detectable in the color that could beovercome by highly efficient top covering surface coverage.

In some embodiments the binders making up the construction could includeinorganic coating materials, such as silicas, silicates, phosphates,titanates, zirconates, aluminosilicates, and the like. Hybridorganic/inorganic binders such as ceramic binders may also be used.

Such a surface could also be a part of individual roofing granules inplace of, at least in part, those used in surfacing of asphaltcomposition roofing shingles. Also, such layer compositions orconstructions may be used in the surface of interior wall or articlesthat can provide further energy saving by optimizing the solar heatabsorption.

Such constructions could be assembled by processes including coating,extrusion, coextrusion, lamination, or other processes known in the artof producing layered structures. Further examples of application forthis invention will become evident to those who are skilled in the art.

Example

Roofing granules are first coated with an inner coating compositionincluding a thermochromic pigment that changes color from white to blackas temperature drops from T1 to T2. The inner coating composition isthen cured. A second or outer coating composition is applied over thecured inner layer, and the outer coating composition is cured to providean outer layer than is transparent to near infrared radiation. Theinfrared reflectivity of the roofing granules is will be reduced from R1to R2 as the temperature drops from T1 to T2. So, while the granulesreflect more heat in summer time, they will absorb more heat in winter.

Various modifications can be made in the details of the variousembodiments of the processes and articles of the present invention, allwithin the scope and spirit of the invention and defined by the appendedclaims.

1. An exterior surface covering comprising: (a) an outer layer having atransmission coefficient of at least 50 percent for electromagneticradiation in the wavelength rage from 700 nanometers to 2500 nanometers;and (b) an inner layer having a reflectance for electromagneticradiation in the wavelength range from 700 nanometers to 2500nanometers, the reflectance being dependent on a variable parameter, thereflectance varying by a factor of at least 0.5 as the parameter isvaried over a predetermined range.
 2. An exterior surface coveringaccording to claim 1 wherein the reflectance increases with an increasein the parameter over the predetermined range of the parameter.
 3. Anexterior surface covering according to claim 1 wherein the outer layeris colored.
 4. An exterior surface covering according to claim 1 whereinthe variable parameter is temperature.
 5. An exterior surface coveringaccording to claim 4 wherein the inner layer comprises at least onethermochromic substance selected from the group consisting ofthermochromatic colorants, thermochromatic polymers, compositethermochromatic pigments, chromogenic thermotropic gels, vanadiumoxides, polythiophene polymers, liquid crystals, spirobenzopyrans,spironaphthoxazines, chromenes, fulgides, and diarylethenes.
 6. Anexterior surface covering according to claim 4 wherein the reflectancevaries from less than 0.2 to greater than 0.25 when the temperaturevaries from less than 20 degrees C. to greater than 30 degrees C.
 7. Anexterior surface covering comprising: (a) an outer colored layer havinga transmission coefficient of at least 50 percent for electromagneticradiation in the wavelength rage from 700 nanometers to 2500 nanometers;(b) a middle layer having a transmission coefficient for electromagneticradiation in the wavelength range from 700 nanometers to 2500nanometers, the transmission coefficient being dependent on a variableparameter, the transmission coefficient varying by a factor of at least0.5 as the parameter is varied over a predetermined range; and (c) aninner layer having a reflectance of at least 40 percent forelectromagnetic radiation in the wavelength range from 700 nanometers to2500 nanometers.
 8. An exterior surface covering according to claim 7wherein the transmission coefficient of the middle layer increases withan increase in the parameter over the predetermined range of theparameter.
 9. An exterior surface covering according to claim 8 whereinthe variable parameter is temperature.
 10. An exterior surface coveringaccording to claim 9 wherein the middle layer comprises at least onethermochromic substance selected from the group consisting ofthermochromatic colorants, thermochromatic polymers, compositethermochromatic pigments, chromogenic thermotropic gels, vanadiumoxides, polythiophene polymers, liquid crystals, spirobenzopyrans,spironaphthoxazines, chromenes, fulgides, and diarylethenes.
 11. Anexterior surface covering according to claim 8 wherein the transmissioncoefficient of the middle layer varies from less than 0.4 to greaterthan 0.5 when the temperature varies from less than 20° C. to greaterthan 30° C.
 12. An exterior surface covering comprising: (a) an outercolored layer having a transmission coefficient of at least 50 percentfor electromagnetic radiation in the wavelength rage from 700 nanometersto 2500 nanometers; (b) a middle layer having a transmission coefficientfor electromagnetic radiation in the wavelength range from 700nanometers to 2500 nanometers, the transmission coefficient beingdependent on a variable parameter, the transmission coefficient varyingby a factor of at least 0.5 as the parameter is varied over apredetermined range; and (c) an inner layer having an absorptioncoefficient at least 60 percent for electromagnetic radiation in thewavelength range from 700 nanometers to 2500 nanometers.